In the old days, whenever vinyl siding was installed around any
type of obstruction (such as a light fixture, a dryer vent, or an
electrical outlet) a "frame" of J-channel was placed around the
object to conceal the cut edges of the siding. But this practice is
tedious when there are lots of light fixtures or outlets to work
around.

After many years of making vinyl siding, the manufacturers got
wise and started selling a special component called a J-block
that simplifies siding installation around common obstructions.

This is a basic J-block that I bought from
Menard's for about $6.

Unfortunately, Menard's didn't
stock this item in the green color of the siding. Since
this was going on the back of the shed, I didn't care
about the color not matching.

This J-block is a two-part unit. The top
piece just pulls off.

This is a basic outdoor electrical box.

This junction box is supposed to be
mounted using these two metal tabs that screw into the
back.

BUT...

With the mounting tabs, the box
wouldn't fit inside the J-block.

So I drilled four holes in the back of the
outdoor electrical box. These holes were just big enough
to handle the mounting screws I planned on using.

Closer view.

Then I screwed a 3/8" cable clamp to the
hole in the back side of the box.

When the clamp is
fastened over the electrical cable, the screws will
stick out pretty far. The red circle represents the
large hole I will need to drill in
the wall for this clamp to sit inside.

I realized that the clamp would not fit
inside the small hole that is pre-punched in the
J-block, so I marked a larger hole to cut.

I cut out the hole with tin snips and end
nippers.

This is the intended location of the
electrical box.

Lifting Up The Vinyl Siding:

I slipped
the vinyl siding removal tool (also called a
J-hook) under the bottom lip of
the siding panel and pulled the tool downward to release
the siding.

Once the siding was lifted away at the
end, I moved the tool to the right and pulled away the
siding all the way to the far end.

On The Siding Panel Below:

I removed some of the nails so I could reach behind
the siding.

I laid out a notch that was about
¼" bigger than the J-block. Then I used aviation snips
to cut the notch in the siding.

I cut a similar notch in the upper panel
of siding, but the vinyl cracked when I was cutting it.
That's typical of vinyl siding... it cracks when the
temperature is a little cool.

Cut out ready for the J-block.

With
one-piece J-blocks, this project is much easier if
the outlet straddles the joint between two siding
panels.

Since my J-block has a detachable face, I could have
easily put the cut-out in the middle of the
siding panel. However, cutting the hole would have been
trickier.

I slipped the back part of the J-block
into the notch and drove two nails at the top.

I pulled the siding away from the wall and
drove two more nails down low.

Then I nailed the lower piece of siding in
place.

I re-attached the upper piece of
siding using the siding J-tool seen earlier.

I set the electrical box in place and
drilled a small hole through the cable clamp.

The
purpose of this hole is simply to mark the center of the
larger hole.

Then I used a 1½"
spade bit to drill a large hole in the OSB wall
sheathing.

I set the box in place to make sure the
cable clamp would fit inside the hole.

No problem.

I threaded a piece of 12-2G cable through
the hole and into the box. Then I tightened the cable
clamp to hold the cable securely.

Before fastening the
box to the wall, I ran a bead of caulk around the back
of the box. This should keep water from getting inside
the wall.

I set the box in place and drove 4 short
wood screws through the holes that I drilled earlier.

I slipped the outer part of the J-block
over the electrical box and snapped it onto the back
part..

The project after the J-block was
assembled.

Then I fastened this large cover onto the
electrical box. This cover is approved for wet weather
use while a power cord is plugged in to the
outlet.

Older outdoor box covers were never meant to
be used with a cord plugged in while it's raining.